The invention is directed to the field of diagnostic instruments and more particularly to a diagnostic instrument which is suitable for use with the ear or other medical/industrial target in order to accurately determine a temperature or a temperature profile.
Medical diagnostic instruments such as infrared (IR) ear thermometers have traditionally been inaccurate as compared, for example, to thermistor type or mercury thermometers. This inaccuracy is due in large part to the large interrogation area found in the ear canal. This area includes not only the tympanic membrane (TM), but the ear canal walls as well. At present, there is not an adequate method of alerting the user when the instrument is not properly aligned with the TM. Similarly, the presence of foreign matter, such as ear wax, can block a direct line of sight to the TM and seriously affect the results indicated by the instrument. In addition, the narrowness of the ear canal, sometimes having large curves, also tends to prevent a suitable line of sight to the TM.
A basic assumption made in known IR thermometers is that the TM is within an interrogated area and that the TM subtends a specific portion of this interrogated area. Therefore, the manufacturers of these instruments will add a compensation factor arithmetically to the reading of the thermometer to make up for the fact that the device is reading the ear canal wall in addition to the TM. These devices are particularly inaccurate when the ear canal has been cooled, e.g., immediately after a patient has come indoors from the cold outdoors.
Recently, data have become available which demonstrate that the temperature of the TM in the lower anterior quadrant thereof is largely independent of ambient and skin temperature due to its interconnection with the hypothalamus. This temperature is highly representative of the body xe2x80x9ccorexe2x80x9d temperature. The remainder of the TM is not necessarily at the same temperature. It is therefore quite desirable to measure this xe2x80x9chottestxe2x80x9d spot in order to realize a more accurate reading.
Another issue to consider in the use of IR thermometers is how to deal with the IR radiation originating from the ear tip housing. Radiation from the tip housing combines with that of the target, such that temperature variations of the housing can affect the temperature reading from the sensor.
A known method of avoiding this problem is to keep the temperature of the housing isothermal and at a known level, as described in U.S. Pat. No. 4,759,324. In actual practice, however, this is difficult to accomplish, in part because the ear tip is relatively long, leading to axial temperature gradients. In addition, the geometry of the ear canal is such that little radial room is available for insulation, resulting in heat transfer to and from the ear tip housing by the environment.
It is a primary object of the present invention to improve the accuracy of medical diagnostic instruments.
It is a further primary object of the present invention to provide a medical diagnostic instrument which is capable of accurately determining body core temperature.
It is yet another primary object of the present invention to provide a medical diagnostic instrument which is capable of estimating temperature of a target area if a portion thereof cannot be viewed directly; for example, if a portion of the target area is somehow obstructed.
It is yet another primary object of the present invention to provide a means for negating or minimizing the effects of housing or transient temperature changes in a diagnostic medical instrument, such as an IR ear thermometer.
Therefore, and according to a preferred aspect of the invention there is provided a temperature measuring apparatus for interrogating a medical target area, the apparatus comprising:
a plurality of infrared sensors disposed in a sensor array, each of the sensors in the sensor array being capable of providing an output signal indicative of temperature of a portion of a medical target area such that said sensor array cumulatively provides a temperature profile of the medical target area; and
processing means for processing output signals from the sensor array, the processing means including means for determining temperature based on the output signals therefrom.
Preferably, the above apparatus can be utilized in conjunction with an otoscopic or similar device to examine the ear and, more particularly the tympanic membrane wherein the sensor array can identify the blood vessel portions of the tympanic membrane, which may be interconnected with the hypothalamus, to more accurately predict body core temperature independent of thermal effects caused by other parts of the ear.
In a preferred embodiment, the apparatus displays a real time thermal xe2x80x9cpicturexe2x80x9d or image of a medical target area, such as the ear, armpit, or other area in which processing means can detect or alternately predict the xe2x80x9chottestxe2x80x9d spot(s) with a high degree of certainty.
According to a preferred embodiment, the described apparatus can selectively operate in at least two modes; a first mode in which the entire thermal xe2x80x9cpicturexe2x80x9d is analyzed and a second mode in which the hottest spot can be estimated by interpolation or extrapolation through an examination of the thermal gradient of at least a portion of the thermal image of the target area.
If the latter mode is selected, the apparatus can include an indicator which alerts the user that the displayed value is an estimate, along with the probability of the exactness of the displayed estimate.
A feature of the described apparatus is that direct feedback is provided to the user as to whether or not the array is pointing at the intended target (e.g., the tympanic membrane). For example, by displaying real time false color representations of temperature ranges of the sensed area, the user can continue to aim the instrument until the xe2x80x9chotxe2x80x9d spot is optimally positioned near the center of the thermal image. Alternately, and in lieu of a displayed image, the apparatus can include LCDs or other indicators to similarly guide the physician or other user to a target. For example, a green light indicator can be used to provide feedback to a user that the apparatus is aiming closer to an area of highest temperature. Conversely, a red light or other indicator can provide feedback to the user that the field of view of the apparatus is moving away from the hottest portions of the target.
Another feature of the present apparatus is that the apparatus can be calibrated using a known temperature standard to calibrate a single pixel or, if needed, the entire thermal array.
The apparatus can further include a baffle which permits energy only from the baffle and the target of interest to impinge on the sensor array, thereby negating the effects of the housing of the apparatus and of adjoining areas in the vicinity of the target area. This baffle can also be thermally connected to the substrate supporting the sensor array such that baffle is at the same temperature as the sensor array and can therefore be accounted for, such as in calibration.
Preferably, the baffle is located between the sensor array and the nearest lens of the focusing optics. The baffle forms the aperture stop of the system and defines the largest bundle of rays that the optical system can admit to reach the sensor from the target. All rays in this largest bundle originate in the object (target), as is desired. All other incoming rays reach the baffle either from the object or from other sources, such as the ear tip housing, but these rays are stopped by the baffle. Rays originating from the baffle can reach the sensor, but because the baffle is preferably at the same temperature as the sensor, calibration is not affected.
The instrument preferably includes a locator which permits the insertion portion to be positioned a predetermined distance into the ear canal of a patient. An objective lens distally placed in the insertion portion can then obtain an image of the outer ear, the lens being positioned sufficiently within the ear to substantially avoid ear wax, hair, and a bending portion of the ear canal, but prevented from contacting the tympanic membrane. The locator provides repeatability thereby allowing a thermal image to be superimposed for example, with a video image of the same target as captured by a video otoscope.
In addition, a proximal relay lens can be used to focus the image created by the objective lens onto the thermal sensor array, the array being located within the instrument head in conjunction with the baffle, such that the baffle eliminates IR radiation (heat) emanating from other than the target. This optical arrangement provides advantages in that a relatively wide field of view can be maintained to xe2x80x9cseexe2x80x9d the tympanic membrane with a low f# at the detector.
Another feature of the above apparatus is that the pulse of a subject can be accurately detected based on changes in temperature measured temporally once a blood vessel target has been identified.
According to another preferred aspect of the present invention, there is provided an ear thermometer comprising:
a plurality of infrared sensors disposed in a sensor array, each of said infrared sensors being capable of providing an output signal indicative of temperature of a portion of a target area such that said array cumulatively provides a temperature profile of portions of the outer ear; and
processing means for processing output signals from the sensor array, said processing means including means for determining core body temperature based on the output signals therefrom.
According to yet another preferred aspect of the present invention, there is provided a method for accurately determining the temperature of a medical target comprising the steps of:
aiming a sensor array at a medical target, said sensor array comprising a plurality of infrared sensing elements each being capable of providing an output signal indicative of temperature of a portion of said medical target; and
determining the temperature of each said portion of said medical target;
outputting the signals representative of the temperatures of portions of the medical target.
An advantage of the present invention is that a target can be interrogated more accurately without transient thermal effects typically found in the vicinity of a medical target such as within the ear canal.
Another advantage produced by the present invention is that the presence of inflammations, abscesses, ear wax and other obstructions can quickly be identified and compensated for so as to more accurately identify and estimate the hottest temperature(s) of a defined target area.
These and other objects, features and advantages will become apparent from the following Detailed Description which should be read in conjunction with the accompanying drawings.